The subject matter disclosed herein relates to an aircraft rotor head and, more particularly to a stiff in-plane aircraft rotor head.
Fully articulated elastomeric rotor systems are used on many helicopters. These rotor systems utilize elastomeric bearings to accommodate blade flap, lead/lag and pitch motions. The elastomeric bearings are highly reliable, fail-safe (allowing on condition replacement) and low maintenance. The articulated design has the benefit of greatly reducing the flatwise and chordwise bending moments at the blade root end, but the system requires lead/lag dampers to prevent aircraft ground resonance. The dampers are prone to leakage and require frequent overhauls. They are also difficult to package in a low drag rotor system.
Stiff in-plane designs have been used but are typically constructed using lubricated bearings or composite flexural members to accommodate pitch and flap motions, while providing the required edgewise stiffness to achieve a 1st chordwise elastic frequency greater than 1 per rev. These designs do not require dampers because of the high edgewise stiffness of the blades and blade retention and the resulting frequency placement. Accommodating the above-noted design constraints (i.e., the required edgewise stiffness and the 1st chordwise elastic frequency greater than 1 per rev) with a low maintenance elastomeric rotor has been a continuing design challenge. Particularly, the need to carry blade centrifugal forces with an elastomeric bearing while accommodating pitch and flap and restricting lead/lag motions has posed significant difficulties.